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R. J. NASH AND G. H. ALEXANDER.

FLUID PRESSURE MEASURING INSTRUMENT.

APPLICATION FILED DEC, H. 1518.

1,345,870. Patented July 6, 1920,

2 SHEETS-SHEET l.

I'ILVe-mi/ OTS G. H. 14 lax/unwinany R. J. NASH AND G. H. ALEXANDER.

FLUID PRESSURE MEASURING INSTRUMENT.

APP oN FILED DEC. 17. 1918.

1,345,870. at t d uly 6, 1920.

2 SHEETS-SHEET 2.

III' P IIII IHUI II IIIIIIW I IIIIIIIIMIJ I Ivvuenitars R. J. /Ya/sh rlfL ewanver UNITED STATES PATENT OFFICE.

ROBERT JOHN NASH AND GEORGE HENRY ALEXANDER, 0F BIRMINGHAM, ENGLAND,ASSIGNORS TO THE A-N COMPANY LIMITED, 0F BIRMINGHAM, ENGLAND.

FLUID-PRESSURE-MEASURING INSTRUMENT.

Application filed December 17. 1918.

To all "whom it may (:(mr'ern Be it known that we, Romurr JonN NASH,residing at 107 Bristol road. in the city of Birmingham, England, andGnonon IIENRY ALEXANDER, residing at 83% (loleshill street, in the cityof Birmingham, England, subjects of the King of Great Britain andIreland, have invented certain new and useful Improvements Relating to lluid-lressure- Measuring Instruments, of which the following is aspecification.

This invention relates to fluid pressure measuring instruments of thetype in which a fluid operated indicator or recorder can be arranged ata distance from the receptacle or conduit containing the lluid \vhoscpressure is to be measured, and is separated therefrom by a region ofentrapped air or other gas. In its rudimentary form such apparatus whenemployed, for example, for indicating the level of fluid in a tank,consists of a vessel (herein termed a displacelnent chamber) containingentrapped air or other gas, said vessel being in connnunication at itslower end with the lower end of the tank, and at its upper end with oneend of a U tube containing the indicating, liquid. When the air in thetank is under pressure, the other end of the U-tube is connected to theair space in the tank, otherwise it is open to the atmospluire. Somearrangements hitherto proposed have been of little or no commercialvalue. because the length or height of the displacement chamber has beenmade greater than the diameter. This involves comparatively largefluctuations of level (herein termed the datum level) in thedisplacement chamber and in consequence, especially when the air in thetank is put under variable pressure, it becomes impossible to accuratelycalibrate the U-tube in a manner which will suit all levels and pressures in the tank. A constant or practically constant datum level isessential to a successful instrument. This fact has previously beenrecognized and to enable a constant level to be insured the method hasbeen employed of forcing compressed air into the displacement chamber todepress the datum level to a predetermined position before taking areading on the U-tube.

The object of the present invention is primarily to enable a practicallyconstant datum level to be obtained and conveniently Specification ofLetters Patent.

Patented July 6, 1920.

Serial No. 267,216.

restored when occasion requires in a very simple and convenient manner.

The invention comprises the combination with the displacement chamber,of a pipe which serves both to determine the datum level and also as apassage for air to or from the chamber for restoring such level whenrequired.

In the two accompanying sheets of explanatory drawings Figures 1 to 3illustrate diagrammtically three applications of the invention.

The same reference letters in the different views indicate the same orsimilar parts.

In the application of the invention as shown in Fig. l to a fluid levelindicator for use with a petrol or oil tank or receptacle a on a motorvehicle, a shallow c lindrical or other air-tight displacement c amber bis connected by a pipe 0 to the under side of the tank so that theliquid can rise to a certain level in the chamber. This pipe may beopened or closed by a cock (I. In the first instance air is forced outof the displacement chamber by the incoming liquid until the latterreaches the lower end of the vertical pipe 0 projecting downwardly intothe chamber. The liquid can then rise in the pipe to the same height asthe level in the tank but can only rise farther in the chamber to aheight determined by the head of liquid in the tank. Between the surfaceof the liquid and the upper side of the chamber 7) is a region ofentrapped air. The depth of this region is made as small as convenientcon'lpared with the diameter and volume of the region. Consequentlylarge pressure dilfcrences in the chamber are accompanied by but smallvariations of the level. These variations are such that for practicalpurposes they can be disregarded and the level of the liquid cantherefore be regarded as a constant datum level. Within the chamber isanother chamber f of relatively small diameter. This is open at itslower end to the liquid in the displacement chamber, and perforated atits upper end so as to be in communication with the air in the saidchamber. From the smaller chamber a tube 9 of fine bore is taken to oneend of a U-tube h containing the indicating liquid. The function of thesmaller chamber is to avoid or minimize variation of the levels in theU-tube due to surging of the liquid in the displacement can be blown inthrough the pipe 6 periodi cally and restore the original datum level.Or air can be blown into the chamber through a cock Excess air thenescapes through the pipe 6. The latter thus serves both in determiningand in restoring the datum level. It isralso to be noted that the inneropen end of the pipe 0 is flush with the normal datum level of thechamber 6 so that in case the level falls below normal it will beautomatically returned to or constantly maintained normal by liquidflowing into the chamber from the tank a while. if the datum level risesabove normal, air may. be blown into the pipe 0 to restore the originaldatum level.

Although there isno indication when the level rises above the lower endof the tube 0. when in use, air is periodically blown through the tube 6to insure that the datum level is correct. It at any time the observeris doubtful of his gage reading he just blows a small quantity of airthrough the tube e 7 so as to make sure that the datum level is correct.

The displacement chamber can be arranged in any position either below,above, or alongside the tank. When placed above the tank the entrappedair is subject to negative pressure and when placed below to positivepressure. This makes no difference to the operation of the indicatorexcepting that the readings are taken the one case in one limb of theU-tube and inthe other in crease the volume oi air in Z) and conse Vquently the datum level.

To restore the level air is sucked outthrough the pipe 0 or through acock 2.

air to the same to maintain a constant air 7 pressure therein. For thispurpose the tank is connected to the displacement chamber by a shortvertical pipe '0. Air is admitted by the pipe 6.

The end of the gage which in the other forms is open is connected by asmall diameter pipe j to the tank air space. Assuming the liquid to bewithdrawn from the tank under gravity a reduction of air pressure willoccur and cause the level in e to fall. When a certain pressure isreached air will pass down the tube 6 and finding its way to the tank asshown by the bubbles in the diagram will restore the air pressure andsimultaneously 'maintain the full quantity of air required in 0.. if theliquid is'forced from the tank by air pressure the air'necessary formaintaining the pressure on the upper surface of the liquid in a issupplied through 2). Air is admitted to the-tank in a similar mannerwhen the liquid is withdrawn by a suction pump.

The invention is not limited to the arrangements herein described norto'any constructional details as these; may be-widely varied to meetdifferent requirementsl Having thus described our invention wha t weclaim as new and Letters Patent is In fluid pressure measuringinstruments, the combination comprising a closed displacement'chamber incommunication with a body of fluid and containing a quan-' tity ofentrapped air, the he'igh't of the air 7 space above the fluid datumlevel in the chamber being small relatively to the diameter ofthechamber, afiuid gage communicating at one end with the air space in thedisplacement chamber, and a pipe in communication with the fluidin said'chamher, said pipe serving to determine the datum level and also as'apassage for air to or from the chamber tor restoring such level avhenrequired, substantially Y as described.

In tBStlIIlOIlY whereoi' we have signed our names to this specification.

ROBERT JQHN NASH.-

GEORGE HENRY ALEXANDER.

desire to secure by

